Configurable integrated circuit capacitor array using via mask layers

ABSTRACT

A semiconductor device having a plurality of layers and a capacitor array that includes a plurality of individual capacitors. At least one of the plurality of layers in the semiconductor device may be a via layer configured to determine the connections and capacitances of the plurality of individual capacitors in the capacitor array. The semiconductor device may include a metal structure disposed within the device to provide an electromagnetic shield for at least one of the plurality of individual capacitors in the capacitor array.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from co-pending provisional patentapplication Ser. No. 60/548,000, filed Feb. 26, 2004, by the inventorshereof, the entire disclosure of which is incorporated herein byreference.

BACKGROUND

A capacitor is a fundamental two-terminal electronic device that may bemanufactured in an integrated circuit. However, in an integratedcircuit, it is often difficult to realize a well controlled capacitancevalue. The variation that results from the processes involved in thefabrication of integrated circuits may cause the value of a givencapacitor to change by as much as 30% from device to device. Hence,several smaller capacitors are most often used by connecting them inparallel to create one large capacitor. The accuracy of the combinedcapacitance of these smaller capacitors can be better than 0.1%.Therefore, an array of capacitors is commonly used in integratedcircuits. A capacitor array contains a plurality of individualcapacitors positioned in rows and columns to allow for the routing ofsignals within the integrated circuit. One type of capacitor used in anintegrated circuit is a “poly-poly” capacitor, which uses aparallel-plate structure that includes two polysilicon layers.

FIG. 1 illustrates a side view of the semiconductor layers forming astandard poly-poly capacitor in an integrated circuit. The capacitor 100is formed by the polysilicon layers 106 and 108 where an oxide (detailomitted for clarity) between the polysilicon layers is thinner thannormal inter-layer oxides. Beneath the capacitor 100 is a well 104 thatis diffused into the silicon substrate 102. The well 104 is normallyconnected to a low impedance, low noise point in the circuit to helpshield the capacitor from substrate noise. The polysilicon layers 106and 108 are connected to a metal routing layer (metal 1) that is used toconnect the capacitor 100 to other circuit elements or bond pads withinthe integrated circuit. Contact 114 connects the bottom polysiliconlayer 106 to a first metal 1 routing track 110, and contact 116 connectsthe top polysilicon layer 108 to a second metal 1 routing track 112.

FIG. 2 illustrates a top view of the semiconductor layers forming astandard poly-poly capacitor in an integrated circuit. As shown anddescribed above in connection with FIG. 1, the first metal 1 routingtrack 110 is connected to the bottom polysilicon layer 106 by way ofcontact 114. The second metal 1 routing track 112 is connected to thetop polysilicon layer 108 by way of contact 116. Beneath the capacitor100 formed by polysilicon layers 106 and 108 is the well 104 that isdiffused into the silicon substrate 102.

SUMMARY

The present invention provides for a semiconductor device having aplurality of layers and a capacitor array. In exemplary embodiments, theplurality of layers may include three metal layers, two polysiliconlayers, and one via layer. The capacitor array includes a plurality ofindividual capacitors. At least one of the plurality of layers in thesemiconductor device is a via layer configured to determine theconnections and capacitances of the plurality of individual capacitorsin the capacitor array. The semiconductor device may also include aplurality of circuit elements.

In some embodiments, a metal structure is disposed within thesemiconductor device to provide an electromagnetic shield for at leastone of the plurality of individual capacitors in the capacitor array.The metal structure may be a metal layer that is connected to ground.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a side view of the semiconductor layers forming astandard poly-poly capacitor in an integrated circuit.

FIG. 2 illustrates a top view of the semiconductor layers forming astandard poly-poly capacitor in an integrated circuit.

FIG. 3 illustrates an M by N array of capacitors according to at leastsome embodiments of the present invention.

FIG. 4 illustrates a side view of the semiconductor layers forming apoly-poly capacitor according to at least some embodiments of thepresent invention.

FIG. 5 illustrates a top view of the semiconductor layers forming apoly-poly capacitor according to at least some embodiments of thepresent invention.

FIG. 6 provides a schematic diagram representing the parasiticcapacitances formed by a metal shield according to at least someembodiments of the present invention.

FIG. 7 illustrates a side view of the semiconductor layers forming twoadjacent shielded capacitors according to at least some embodiments ofthe present invention.

FIG. 8 illustrates a top view of the metal 1 layer of two adjacentshielded capacitors according to at least some embodiments of thepresent invention.

FIG. 9 illustrates a top view of the metal 2 and 3 layers of twoadjacent shielded capacitors according to at least some embodiments ofthe present invention.

FIG. 10 illustrates an array of capacitors according to at least someembodiments of the present invention.

FIG. 11 illustrates the metal 2 and 3 layers of an array of capacitorsaccording to at least some embodiments of the present invention.

DESCRIPTION

It is to be understood that the present invention is not limited to theexample embodiments disclosed herein. The meaning of certain terms asused in the context of this disclosure should be understood as follows.The term “metal layer” refers to any layers that are used to makeconnections between various elements within a device. The metal layersmay contain actual metal routing traces, contacts, or vias. A via may beformed by etching material as defined by a mask layer in the fabricationprocess or direct exposure to an electron beam. The resulting hole fromthe etching is then filled by metal and is used to verticallyinterconnect between metal layers in an integrated circuit. Other termswill either be discussed when introduced, or otherwise should be assumedto have the conventional meaning as understood by persons of ordinaryskill in the semiconductor arts.

A semiconductor device according to an embodiment of the presentinvention comprises a plurality of layers and a capacitor array composedof a plurality individual capacitors that are arranged in an organizedmanner such as rows and columns. Capacitance value and interconnectionof both terminals of the capacitors to other circuit elements isconfigured by the via layers during the manufacturing process. FIG. 3illustrates an integrated circuit 300 containing an M by N array 302 ofcapacitors. The capacitors may be connected together using horizontaland vertical routing tracks. These routing tracks are formed ofsegmented wires of fixed length that may be connected end-to-end throughvias, which are shown in more detail in FIG. 4. The combined capacitorsformed by the configuration of the array may be interconnected to othercircuit elements or bond pads within the integrated circuit. In oneimplementation of the invention, a capacitor array may be configured andthe signals routed using a single via layer defined by one mask of themanufacturing process. Discussion of the use of via masks andprogrammable vias to customize a semiconductor device can be found inU.S. Pat. No. 6,580,289, which is incorporated herein by reference.

A device according to the present invention may be realized in varioussemiconductor processes including but not limited to CMOS, BiCMOS, SiGE,GaAs, and HBT. The individual capacitors of the array may be formed withtechniques including but not limited to PIP(polysilicon-insulator-polysilicon) and MIM (metal-insulator-metal).Each capacitor has two metal contacts with one on the top plate and theother on the bottom plate. Each capacitor contact may have the relatedrouting defined by vias. While the specific embodiments of the presentinvention described herein illustrate capacitors comprising twopolysilicon layers, any semiconductor process with a means to realizecapacitors using various layers, such as for example two metal layers,and other layers for routing and/or shielding can be used.

FIG. 4 is an embodiment of the present invention illustrating a sideview of the semiconductor layers forming a poly-poly capacitor using aCMOS process. A capacitor 400 is formed by polysilicon layers 406 and408 where an oxide (detail omitted for clarity) between the polysiliconlayers is thinner than normal inter-layer oxides. Beneath the capacitor400 is a well 404 that is diffused into a silicon substrate 402. Thewell 404 is connected to a low impedance, low noise point in thecircuit, such as analog ground, to help shield the capacitor 400 fromsubstrate noise. The polysilicon layers 406 and 408 are connected to ametal routing layer (metal 2) that is used to connect the capacitor 400to other circuit elements or bond pads within the integrated circuit.The bottom polysilicon layer 406 is connected to a first metal 2 routingtrack 418 by way of contact 414 and via 420. The top polysilicon layer408 is connected to a second metal 2 routing track 426 (see FIG. 5) byway of contact 416 and via 422.

A semiconductor device according to the present invention may include anarrangement of the capacitor array relative to a metal structure thatprovides electromagnetic shielding of the capacitor array or anindividual capacitor within the capacitor array from other layers of theintegrated circuit. The shielding allows signals to be routed aboveand/or below the capacitor array resulting in higher utilization of theintegrated circuit area.

When using a capacitor array, parasitic capacitances can result from thesignal routing that is used to interconnect the individual capacitors.In order to minimize the effects of these parasitic capacitances, ashield can be formed over the capacitor 400 using a metal shield layer(metal 1) 410. Openings are provided in the metal shield layer 410 thatallow the top polysilicon layer 408 and the bottom polysilicon layer 406to connect to the metal 2 layer for routing purposes. The metal shieldlayer 410 is connected to a low impedance, low noise point in thecircuit, such as analog ground, by way of via 424 and a third metal 2routing track 428 (see FIG. 5).

FIG. 5 illustrates a top view of the semiconductor layers of a poly-polycapacitor as shown and described in connection with FIG. 4. The firstmetal 2 routing track 418 is connected through the opening in the metalshield layer 410 to the bottom polysilicon layer 406 by way of via 420and contact 414 (see FIG. 4). The second metal 2 routing track 426 isconnected through the opening in the metal shield layer 410 to the toppolysilicon layer 408 by way of via 422 and contact 416 (see FIG. 4).The third metal 2 routing track 428 is connected to ground and the metalshield layer 410 by way of via 424. Beneath the capacitor 400 formed bypolysilicon layers 406 and 408 is the well 404 (see FIG. 4) that isdiffused into the silicon substrate 402.

FIG. 6 provides a symbolic representation of the parasitic capacitancesformed by the shield using the metal shield layer as shown and describedin connection with FIG. 4. Capacitor 602 (C1) represents the capacitorformed by the polysilicon layers 406 and 408 (see FIG. 4). Capacitor 604(C2) represents the parasitic capacitance formed by the metal shieldlayer 410 and the top polysilicon layer 408 (see FIG. 4). Capacitor 606(C3) represents the parasitic capacitance formed by the metal shieldlayer 410 and the bottom polysilicon layer 406 (see FIG. 4). Capacitor608 (C4) represents the parasitic capacitance formed by the bottompolysilicon layer 406 and the well 404 (see FIG. 4). As shown in FIG. 6,all of the parasitic capacitances are connected to ground, which allowsfor the effective utilization of the shield in parasitic insensitiveswitched capacitor circuits where any capacitance to ground iseffectively cancelled. Using a shielded capacitor as shown and describedin FIGS. 4 and 5, it is possible to create a capacitor array with moreflexibility in the routing of signals.

FIG. 7 is an embodiment of the present invention illustrating a sideview of the semiconductor layers forming two adjacent shieldedcapacitors. A first capacitor 700 is formed by polysilicon layers 706and 708 where an oxide (detail omitted for clarity) between thepolysilicon layers is thinner than normal inter-layer oxides. Beneaththe capacitor 700 is a well 704 that is diffused into a siliconsubstrate 702. The well 704 is connected to a low impedance, low noisepoint in the circuit, such as analog ground, to help shield thecapacitor 700 from substrate noise. The polysilicon layers 706 and 708are connected to a first metal routing layer (metal 2) that is used toconnect the capacitor 700 to other circuit elements or bond pads withinthe integrated circuit. The bottom polysilicon layer 706 is connected toone of the metal 2 routing tracks 718 by way of contact 714 and via 722.The top polysilicon layer 708 is connected to at least one of the metal2 routing tracks 718 by way of contact 716 and via 724. To providemaximum routing flexibility within the integrated circuit, a secondmetal routing layer (metal 3) is provided. The metal 2 and metal 3layers maybe interconnected using a programmable via layer 730. Insupport of the first capacitor 700. the programmable via layer 730includes via 732 stacked atop via 722 and connecting to metal 3 routingtrack 728, and partially hidden via 734 stacked atop via 724 connectingto another (hidden) metal 3 routing track (compare with via 420 stackedatop contact 414 and partially hidden via 422 stacked atop contact 416.in FIGS. 4 & 5).

Segments of a metal shield layer (metal 1) are used to form a shield forthe individual capacitors. The shield is formed over the first capacitor700 using a first metal 1 shield segment 710. Openings are provided inthe metal 1 shield segment 710 that allow the top polysilicon layer 708and the bottom polysilicon layer 706 of the first capacitor 700 to beconnected to the metal 2 layer for routing purposes. The first metal 1shield segment 710 is connected to a low impedance, low noise point inthe circuit, such as analog ground, by way of via 720 and at least oneof the metal 2 routing tracks 718. While the metal shield layer in thisembodiment is shown as being divided into a plurality of segments thatare used to shield various individual capacitors, the metal shield layermay be one complete or partial layer over the entire device or capacitorarray or a portion thereof.

A second capacitor 701 is formed by polysilicon layers 707 and 709 wherean oxide (detail omitted for clarity) between the polysilicon layers isthinner than normal inter-layer oxides. Beneath the capacitor 701 is thewell 704 that is diffused into the silicon substrate 702. Thepolysilicon layers 707 and 709 are connected to the first metal routinglayer (metal 2) that is used to connect the capacitor 701 to the othercircuit elements or bond pads within the integrated circuit. The bottompolysilicon layer 707 is connected to at least one of the metal 2routing tracks 718 by way of contact 715 and via 725. The toppolysilicon layer 709 is connected to at least one of the metal 2routing tracks 718 by way of contact 717 and via 723. In support of thesecond capacitor 701, the programmable via layer 730 includes via 735stacked atop via 725 and connecting to metal 3 routing track 728, andpartially hidden via 733 stacked atop via 723 and connecting to another(hidden) metal 3 routing track (compare with via 420 stacked atopcontact 414 and partially hidden via 422 stacked atop contact 416, inFIGS. 4 & 5). As a result, capacitors 700 and 701 are connected inparallel with their bottom polysilicon layers 706, 707 connected tocommon metal 3 routing track 728 and their top polysilicon layers 708,709 connected to another (hidden) common metal 3 routing track.

A shield is formed over the second capacitor 701 using a second metal 1shield segment 711. Openings are provided in the second metal 1 shieldsegment 711 that allow the top polysilicon layer 709 and the bottompolysilicon layer 707 of the second capacitor 701 to be connected to themetal 2 layer for routing purposes. The second metal 1 shield segment711 is connected to a low impedance, low noise point in the circuit,such as analog ground, by way of via 721 and at least one of the metal 2routing tracks 718.

FIGS. 8 and 9 illustrate a top view of the semiconductor layers formingtwo adjacent shielded capacitors as shown and described in connectionwith FIG. 7. The two adjacent shielded capacitors form a 1×2 capacitortile. FIG. 9 illustrates the metal 2 routing tracks 718 and the metal 3routing tracks 728 that may be used to connect capacitors 700 and 701(see FIG. 7) to each other or to other circuit elements or bond padswithin the integrated circuit. In the embodiment as shown, there is arouting grid of sixteen vertical metal 2 routing tracks 718 that runperpendicular to eight horizontal metal 3 routing tracks 728, whichforms a routing fabric. All of the direct connections are made to thecapacitors 700 and 701 using the metal 2 routing tracks 718. Theremaining metal 2 routing tracks 718 and all of the metal 3 routingtracks 728 can be used for signal routing. The interconnections betweenthe metal 2 and metal 3 layers may be accomplished using vias, such asthe programmable vias described in connection with FIG. 7, where thevertical and horizontal routing tracks cross each other. Thus, FIG. 7,FIG. 8, and FIG. 9 together illustrate both a structure and a method ofassembling example embodiments of the invention. Using programmable viasto interconnect the metal 2 and metal 3 layers can be automated;therefore, no manual signal routing may be required.

In FIG. 8, the polysilicon layers 706 and 708 of the first capacitor 700(see FIG. 7) and the polysilicon layers 707 and 709 of the secondcapacitor 701 (see. FIG. 7) are connected to the metal 2 routing tracks718 (see. FIG. 9) that may be used to connect the first capacitor 700and the second capacitor 701 to each other or to other circuit elementsor bond pads within the integrated circuit. At least one of the metal 2routing tracks 718 is connected through an opening in the first metal 1shield segment 710 to the bottom polysilicon layer 706 by way of via 722and contact 714 (see FIG. 7). At least one of the metal 2 routing tracks718 is connected through an opening in the first metal 1 shield segment710 to the top polysilicon layer 708 by way of via 724 and contact 716(see FIG. 7). Additionally, at least one of the metal 2 routing tracks718 is connected to ground and the first metal 1 shield segment 710 byway of via 720. Beneath the capacitors 700 and 701 is the well 704 (seeFIG. 7) that is diffused into the silicon substrate 702. At least one ofthe metal 2 routing tracks 718 is connected through an opening in thesecond metal 1 shield segment 711 to the bottom polysilicon layer 707 byway of via 725 and contact 715 (see FIG. 7). At least one of the metal 2routing tracks 718 is connected through an opening in the second metal 1shield segment 711 to the top polysilicon layer 709 by way of via 723and contact 717 (see FIG. 7). At least one of the metal 2 routing tracks718 is connected to ground and the second metal 1 shield segment 711 byway of via 721.

FIGS. 10 and 11 illustrate an array of capacitors formed using multiple1×2 capacitor tiles. As shown and described in connection with FIGS. 7,8 and 9 above, two adjacent shielded capacitors may be used to form a1×0.2 capacitor tile. FIGS. 10 and 11 illustrate how the 1×2 capacitortiles can be arranged into an array of any practical size (typicallyless than 1000 units) by simply alternating the orientation of the metal2 and metal 3 routing tracks. FIG. 10 illustrates an arrangement ofcapacitors 1000 such as those shown and described in connection withFIG. 7 above. A routing fabric 1100 is illustrated in FIG. 11. Therouting fabric 1100 is composed of 1×2 capacitor tiles wherein theorientation of the metal 2 routing tracks 1102 is alternated from onecapacitor tile to the next to permit the routing of signals throughoutthe array. The metal 3 routing tracks 1104 are also alternated from onecapacitor tile to the next for the same purpose. As seen in the top viewof FIG. 11, in routing fabric 1100, the metal 2 routing tracks 1102 aassociated with one capacitor tile 1110 are aligned with the metal 3routing tracks 1104 a associated with an adjacent capacitor tile 1120,and the metal 3 routing tracks 1104 a associated with capacitor tile1120 are aligned with the metal 2 routing tracks 1102 b associated withadjacent capacitor tile 1130. Thus, in the top view, routing fabric 1100comprises rows 1106 of collinear routing tracks extending in bothdirections, with adjacent aligned routing tracks meeting at junctions1108. To permit the routing of signals throughout the array. connectionsare formed in the aforementioned via layer at these junctions 1108.

Specific embodiments of an invention are described herein. One ofordinary skill in the semiconductor arts will quickly recognize that theinvention has other applications in other environments. In fact, manyembodiments and implementations are possible. The following claims arein no way intended to limit the scope of the invention to the specificembodiments described above.

1. A semiconductor device comprising: a capacitor array comprising aplurality of capacitor tiles, each capacitor tile comprising at leastone capacitor; a first plurality of first metal routing tracksoverlaying the at least one capacitor of each capacitor tile; a secondplurality of second metal routing tracks also overlaying the at leastone capacitor of each capacitor tile, with the second metal routingtracks crossing over the first metal routing tracks; an orientation ofthe first metal routing tracks being alternated from one capacitor tileto the next; and an orientation of the second metal routing tracks beingalternated from one capacitor tile to the next; each capacitor within acapacitor tile having: a first electrical connection to a first of saidfirst metal routing tracks and a second electrical connection to asecond of said first metal routing tracks; and a plurality of vias allbelonging to a single layer within the semiconductor device, saidplurality of vias connecting some of the second metal routing tracks tosome of the first metal routing tracks, such that capacitors belongingto different capacitor tiles are electrically connected to one anotherby the second metal routing tracks to thereby form a combined capacitor.2. The semiconductor device according to claim 1, wherein: eachcapacitor tile comprises two capacitors arranged in a 1×2 configuration.3. The semiconductor device according to claim 1, wherein: saidplurality of vias are located where the second metal routing trackscross over the first routing tracks.
 4. The semiconductor deviceaccording to claim 1, wherein: in a top view: the first metal routingtracks associated with one capacitor tile are aligned with the secondmetal routing tracks associated with an adjacent capacitor tile, suchthat the device comprises rows of collinear routing tracks.
 5. Thesemiconductor device according to claim 4, wherein: in said top view:adjacent collinear routing tracks meet at junctions where connectionsare formed in said single layer to thereby permit routing of signalsthroughout the capacitor array.
 6. The semiconductor device according toclaim 1, wherein: the first metal routing tracks associated with a givencapacitor tile are all parallel to one another and have a firstorientation; and the second metal routing tracks associated with saidgiven capacitor tile are all parallel to one another and have a secondorientation, the second orientation being perpendicular to the firstorientation.
 7. The semiconductor device according to claim 1, furthercomprising: a metal structure disposed to provide an electromagneticshield for a plurality of said capacitor tiles.
 8. The semiconductordevice according to claim 7, wherein: the metal structure is connectedto ground.
 9. The semiconductor device according to claim 7, wherein:the metal structure comprises a metal layer.
 10. The semiconductordevice according to claim 7, wherein each of said first and secondelectrical connections comprises: a contact from a polysilicon layer ofan individual capacitor to the metal structure; and a via from the metalstructure to one of said first metal routing tracks.
 11. Thesemiconductor device according to claim 1, comprising: a plurality oflayers including at least three metal layers, at least two polysiliconlayers, and said single via layer.
 12. The semiconductor deviceaccording to claim 1, further comprising: a plurality of circuitelements.
 13. The semiconductor device according to claim 1, wherein:the device is an integrated circuit.
 14. A semiconductor devicecomprising: a two-dimensional arrangement of capacitor tiles, eachcapacitor tile comprising: at least one capacitor; a first plurality offirst metal routing tracks overlaying the at least one capacitor; asecond plurality of second metal routing tracks also overlaying the atleast one capacitor, with the second metal routing tracks crossing overthe first metal routing tracks, a first electrical connection from saidat least one capacitor to a first of said first metal routing tracks;and a second electrical connection from said at least one capacitor to asecond of said first metal routing tracks; wherein: an orientation ofthe first metal routing tracks is alternated from one capacitor tile tothe next; an orientation of the second metal routing tracks isalternated from one capacitor tile to the next; and a plurality of viasall belonging to a single layer within the semiconductor device connectsome of the second metal routing tracks to some of the first metalrouting tracks, such that capacitors belonging to different capacitortiles are electrically connected to one another by the second metalrouting tracks to thereby form a combined capacitor.
 15. Thesemiconductor device according to claim 14, wherein: each capacitor tilecomprises two capacitors arranged in a 1×2 configuration.
 16. Thesemiconductor device according to claim 14, wherein: said plurality ofvias are located where the second metal routing tracks cross over thefirst routing tracks.
 17. The semiconductor device according to claim14, wherein: in a top view: the first metal routing tracks associatedwith one capacitor tile are aligned with the second metal routing tracksassociated with an adjacent capacitor tile, such that the devicecomprises rows of collinear routing tracks.
 18. The semiconductor deviceaccording to claim 17, wherein: in said top view: adjacent collinearrouting tracks meet at junctions where connections are formed in saidsingle layer to thereby permit routing of signals throughout thecapacitor array.
 19. The semiconductor device according to claim 14,wherein: the first metal routing tracks associated with a givencapacitor tile are all parallel to one another and have a firstorientation; and the second metal routing tracks associated with saidgiven capacitor tile are all parallel to one another and have a secondorientation, the second orientation being perpendicular to the firstorientation.
 20. The semiconductor device according to claim 14, furthercomprising: a metal structure disposed to provide an electromagneticshield for a plurality of said capacitor tiles.
 21. The semiconductordevice according to claim 20, wherein: the metal structure is connectedto ground.
 22. The semiconductor device according to claim 20, wherein:the metal structure comprises a metal layer.
 23. The semiconductordevice according to claim 20, wherein each of said first and secondelectrical connections comprises: a contact from a polysilicon layer ofan individual capacitor to the metal structure; and a via from the metalstructure to one of said first metal routing tracks.
 24. Thesemiconductor device according to claim 14, comprising: a plurality oflayers including at least three metal layers, at least two polysiliconlayers, and said single via layer.
 25. The semiconductor deviceaccording to claim 14, further comprising: a plurality of circuitelements.
 26. The semiconductor device according to claim 14, wherein:the device is an integrated circuit.